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Associated Press

Michigan U.S. Rep. John Conyers is warning about dangers from storing piles of an oil-refining byproduct known as petroleum coke near the Detroit riverfront.

The Detroit Democrat said Tuesday that the “unsightly mountain of petroleum coke” is an eyesore for Detroit as well as for residents of nearby Windsor, Ontario.

MLive.com reports that Conyers and fellow Democratic U.S. Rep. Gary Peters have written the Michigan Department of Environmental Quality to investigate whether Detroit Bulk Storage is complying with state regulations for storing petroleum coke.

The department has said in the past that it doesn’t see an immediate environmental threat.

The petroleum coke piles result from Marathon Oil’s refining exports from oil sands in Alberta.